1. Field of Invention
The present invention relates to a projection system, a projection lens module, an actuator and a driving method of the actuator. More particularly, the present invention relates to a projection system, a projection lens module, an optical actuator and a driving method of the optical actuator.
2. Related Art
In general, an optical actuator is applied to a projection system in order to increase the number of pixels and smooth an image. The projection system includes an image generating device and a projection lens module. The image generating device generates the image according to the technology of digital micro-mirror devices (DMDs), three liquid crystal displays (3LCD) or liquid crystal on silicon (LCoS) panels. Then, the projection lens module projects the image onto a screen. The optical actuator is disposed between the image generating device and the projection lens module, and swings to increase the number of pixels and smooth the image.
The optical actuator may be a reflective or transmissive actuator. The transmissive optical actuator is disposed between the image generating device and the projection lens module. The reflective optical actuator is disposed at the projection lens module. After the image generating device generates the image, the image will be transferred to the optical actuator.
However, the transmissive optical actuator is not commercialized under the spatial limitation and the large swinging angle which has to be 50 times of that of the reflective optical actuator.
There are two conventional methods of controlling the reflective optical actuator to operate. The first method is performed according to pulse width modulation (PWM) in conjunction with the feedback of a photo detector, while the second method is performed by controlling the optical actuator using a specific waveform without the feedback control. When the first method is used, the optical actuator can have lower structural rigidity so that the driving force may be smaller. However, the drawback is that the feedback control is needed.
A driving signal W1 with the specific waveform is shown in FIG. 1 and has an initial section W11, a varying section W12 and a target section W13. The initial section W11 drives the optical actuator to keep at one position, the target section W13 drives the optical actuator to keep at the other position, and the varying section W12 drives the optical actuator to shift between the two positions. When the second method is used, no feedback control is needed, but the optical actuator needs to have higher structural rigidity so that the driving force has to be larger and the damping property is needed to decrease the residual vibration after it has reached the position.